In an engine, lubrication is applied to those parts of a cylinder block and a cylinder head, which require lubrication, in order to maintain the functions of such parts. Specifically, as shown in FIG. 13, an engine 102 comprises a cylinder block 104, a crank lower case 106, an oil pan 108, a cylinder head 110, and a cylinder head cover (not shown) for defining a cam chamber when placed on the cylinder head 110. Between the cylinder block 104 and the crank lower case 106, a crankshaft 112 is axially supported. On an upper part of the cylinder head 110, an inlet side and an outlet side are coacted with a camshaft housing (not shown) having an integral structure therewith, and a first-side camshaft 114 located on one side, as well as a second-side camshaft (not shown) located on the other side, is axially supported. The rotations of the first-side camshaft 114 and the second-side camshaft (not shown) actuate a first-side hydraulic adjuster (HLA) 116 located on one side of the cylinder head 110 and a second-side hydraulic adjuster (not shown) located on the other side to cause an inlet valve 118 and an outlet valve (not shown) to move reciprocally. The first-side hydraulic adjuster 116 is provided with a high pressure chamber 116a.
In order to feed lubrication oil to the engine 102, an oil pump 120 is mounted on the crank lower case 106. The oil pump 120 draws the lubrication oil in the oil pan 108 from an inlet tube 124 though a strainer 122, and feeds it, under pressure, to those parts which require lubrication, such as the first-side hydraulic adjuster 116, the second-side hydraulic adjuster, a cam journal (not shown) of the camshaft housing via first and second block side oil passageways 126 and 128 which are formed in the cylinder block 104 and first and second head side oil passageways 130 and 132 which are formed in the cylinder head 110. By this, lubrication is applied to various parts of the engine 102.
A structure of a cylinder head of this type is disclosed, for example, in Japanese Laid-Open Patent Application No. Hei 1-253552. As shown in FIG. 14, the structure described in this official publication has an oil feed passageway 204 formed in a generally central part of a cylinder head 202 of an engine, the oil feed passageway 204 being in communication with a reserve chamber 206 formed in an upper part of the cylinder head 202, the reserve chamber 206 being, in turn, communicated with an adjuster oil passageway 210 which is in communication with an adjuster guide portion 208 and a second-side adjuster oil passageway 214 which is in communication with a second-side adjuster guide portion 212. A plug 216 for sealing the reserve chamber 206 is formed with an air removing hole 218 for discharging air (air bubble) generated in the oil passageways.
Incidentally, in the structure of a cylinder head according to the prior art, if air (air bubble) is contained in the lubrication oil in the oil passageways, which is fed under pressure by an oil pump, the lubrication oil is supplied to those parts which require lubrication such as a hydraulic adjuster, etc., together with this air. In this way, when the air-containing lubrication oil is supplied, for example, to the hydraulic adjuster, the air enters the high pressure chamber of the hydraulic adjuster to create a sponge-like condition. As a result, a foreign sound is generated in the engine due to poor operation of the hydraulic adjuster. When the engine is operated for a long time or at a high speed in such a condition as just mentioned, the hydraulic adjuster, the inlet valve, etc. are damaged.
Therefore, in order to obviate the above inconveniences, according to the present invention there is firstly provided a structure of a cylinder head assembly having a camshaft axially supported by a cylinder head through a camshaft housing and a head oil passageway for guiding a lubrication oil to those parts of the cylinder head which require lubrication, the structure of the cylinder head assembly being characterized in that the camshaft housing is provided with an oil reserve chamber communicating with the head oil passageway.
Secondly, there is provided a structure of a cylinder head assembly having a camshaft axially supported by a cylinder head through a camshaft housing and a head oil passageway for guiding a lubrication oil to those parts of the cylinder head which require lubrication, the structure of the cylinder head assembly being characterized in that the camshaft housing is provided with an oil reserve chamber communicating with the head oil passageway, one end of a through-passageway being communicated with an upper part of the oil reserve chamber and the other end thereof being communicated with a camshaft journal of the camshaft housing.
According to the construction of the present invention, firstly, since the oil reserve chamber is formed in the camshaft housing, the number of parts can be avoided from increasing, the camshaft housing can be improved in rigidity, and machinability can be improved.
Secondly, the air, which remains in an upper part of the oil reserve chamber due to stopping of the engine, is supplied to the camshaft journal side via the through-passageway when the engine is driven. As a result, the air is not supplied to such parts as the hydraulic adjuster, etc., and therefore the functions of the parts such as the hydraulic adjuster, etc. are maintained in a favorable condition to ensure a favorable operation of the engine. Furthermore, since the through-passageway acts as means for removing the air in the oil reserve chamber and feeding the lubrication to the camshaft journal, the lubrication oil can be effectively utilized.